1. operating system. 2. [obsolete, ITS], an output spy. See "OS and JEDGAR". 3. An operating system from IBM for their System/360 line of hardware announced in 1964. OS was planned with several flavours that were supposed to be compatible. OS was late, memory hungry and not able to reach the marketing objectives of IBM for the 360/30, the planned successor of the IBM 1401. IBM then decided to design a new operating system for the low end machines which they called DOS/360. [Jargon File] (1997-09-22)

Os

(Os), chemical element, one of the platinum metals of Group VIIIb of the periodic table and the densest naturally occurring element. A gray-white metal, osmium is very hard, brittle, and difficult to work, even at high temperatures. Of the platinum metals it has the highest melting point, so fusing and casting are difficult. Osmium wires were used for filaments of early incandescent lamps before the introduction of tungsten. It has been used chiefly as a hardener in alloys of the platinum metals, though ruthenium has generally replaced it. A hard alloy of osmium and iridium has been used for tips of fountain pens and phonograph needles, and osmium tetroxide is used in certain organic syntheses.